A few years ago I created a modification to the 42005 Monster Truck set, where I motorized it and made it RC (IR), but tried to keep the geometry as close to the original set as possible (see topic here).
I always liked the design and size of the body of this truck, so I have used it again, but this time I have completely removed the chassis and the drivetrain, and inserted a new one.
This truck uses:
the Lego Power Functions Rechargeable Battery (8878)
to power an SBrick
which controls a 9V Buggy Motor (5292) for drive
and a Power Functions Servo Motor (88004) for steering.
The truck is controlled remotely using Bluetooth via the SBrick and SBrick Android App on my mobile phone.
This truck features:
large suspension travel
Ackermann Steering
and positive caster steering geometry.
The tires (56908c03) are the tires that were first seen in the Batman Tumbler set (76023).
Even though the wheels are so far apart the truck has a short wheelbase, and thanks to the Ackermann steering geometry and differential in the rear it has a fairly tight turning circle.
The front suspension uses a single shock absorber (731c05) with a setup similar to the 8081 Extreme Cruiser set from 2011.
The rear independent suspension uses two hard shock absorbers (731c04), one each side.
Here's a video to see it in action:
Although the Monster truck uses a Buggy Motor, I couldn't give it full power without the battery and/or SBrick cutting power to it. I could only go at about 70% of max speed, and that is using the slower output of the Buggy Motor too. I didn't have much space for gear reduction (apart from a 20-tooth gear to 28-tooth differential), so the output doesn't have much torque when using such large tires. Because of this, the truck takes a while to get to full speed, and slows down when hitting an incline or going off-road, which kind of makes the large suspension travel a bit pointless. I might see if I can gear it down some time in the future.
I still continue to have a lot of trouble with the SBrick too. I finally have a version of the SBrick Android App that seems to work ok, but despite being only a few feet away and with nothing else around to interfere with it, it would still lose connection with my SBrick regularly. Hopefully BuWizz will be better, and be able to power the Buggy Motor better too.
My BrickShelf Gallery with larger images (once moderated)
Any constructive feedback/comments/questions are welcome.

Thanks. I thought that you would like the drivetrain images
The distance that the string moves is dictated by the cranks. I used 'Technic, Liftarm 2 x 4 L-Shape Thick' because a Liftarm 4 was too short, and a Liftarm 5 was too long. However, the Liftarm 2 x 4 L-Shape is just a fraction too long too, so when the ladder reaches the top of it's movement the rubber bands stretch ever-so-slightly. You can see this in the video at 1:56 (https://youtu.be/XQCGHxT8XaE?t=1m56s), but is only a very slight movement. Before I had finalised the design, the rubber bands were needed more, but I could probably get away without using them now.
If I make it to BrickVention I could bring the parts needed and build it there if I have time (I have already bought my tickets to the convention, but still need to finalise things in the US before moving back to Australia).
Thanks Lego_GBC_NL
If you do end up building it, please post a pic or video for us to see.

Hi Everyone.
I have created an LDraw/MLCad file of my GBC module.
>> Download Here <<
While creating this CAD file, I noticed a few things that I would like to change in the model, however I have kept the CAD file matching the model at this stage.
While I have added steps in the CAD file, the file is mainly organised with submodels that make it easier to organise rather than build.
That is, submodels are added whenever there is an odd angle change, and the drivetrain is separate from the frame and electricals.
The toughest parts to make in MLCad were the chain/s and the string/s.
The chain links don't quite line up, so on the bottom the links are slightly out of alignment.
I think that I did a pretty good job with the string, although I did need to add lots of submodels in the CAD file.
In the following image you can see how the GBC breaks down into 4 distinct sections:
Here are a few more images of each section and their drivetrains:
If someone would like to download and review the LDraw/MLCad file and let me know if any changes are needed, that would be appreciated (I'm sure there are a few mistakes that I missed ).
>> Download Here <<
This CAD file provides enough information for me if I ever wanted to rebuild the "To and Fro" GBC module, but if someone wants to turn it into a full set of instructions, please do so, and add a link in this topic.
Any constructive feedback/comments/questions are welcome.
My Brickshelf Gallery with larger images (once moderated)

Hi Roland. I am still running v1.6 Alpha 4. I updated the main.cfg file as suggested in your FAQ. When opening LDCad, I can now see the screen (no more black area), but as soon as I go to the Nested tab it freezes for a few seconds, and then the same thing happens as before where the interface items (menu/toolbar/compass/etc) disappear again. This happens in both 32 bit and 64 bit.
I have already gone ahead and made my chains and string in MLCad. They don't line up 100%, but are close. I should be finished with the MLCad file in the next day or so.

Hi Roland. I am trying to use the Technic Chain template (part 3711). I'm running Windows 7 64 bit, OpenGL 2.1.0 (I don't have permissions to update this). I have also downloaded/unzipped v1.6 Alpha 4 and tried both 32 bit and 64 bit versions, but all I can see is the status bar and all of the rest of the screen is black. I can still mouse over items and see the description in the status bar, but I am basically running blind.

Hi Philo. I tried to follow your advice, but I'm having a lot of trouble with LDCad (v1.5). I don't find the software very intuitive at all, but I'm sure that I just have to get used to it over time. I read through the documentation and thought that I would try to create a chain. As soon as I add a template part (chain) and then go to nested mode, the software bugs out and half of the interface disappears, including the menu, the toolbar, the compass, the pin, etc, making the software even harder to use. The same happens if I try to edit the chain submodel directly. I can't see the little yellow spheres that the documentation says are needed to be able to create the custom sized chain, so I can't resize my chain at all. For the time being I think that I'm giving up on LDCad.

Does this help?
Under normal load, the tan spider gears within the differential spin at the same speed but in opposite directions, but the differential cage doesn't spin.
Under excessive load, the clutch slips, causing the spider gears to spin at different speeds, and that causes the differential cage to spin (a tiny bit).
When the differential cage spins, it tuns the 16-tooth gear down the bottom, which rotates the black 2L liftarm, which moves the yellow liftarm and the other black 2L liftarm on the left, and that is attached to the first switch (which turns on the alarm).
The tops of the switches are linked so that only one switch can be turned on at a time.
Let me know if you have any further questions.
For a purely mechanical solution, would something like the mechanism in this ladybug work?
I have a few other ideas too, but I'd have to build them to see if they would work. I'll see what I can come up with.
PS. Are you going to Brickvention in Melbourne in January 2017?

Thanks everyone for your kind comments
The 'Automatic Motor Shutoff and Alarm System' seems to be popular. The nice thing about it is that under normal use it just passes through the motor's power with very little added resistance. The gear ratio doesn't change either, so it is easy to replace any existing motor with this system without having to make any major modifications. The clutch in the middle only slips for a split second before the motor turns off, so the parts used to make the clutch aren't being worn out either. It is great for mechanisms that have constant loads on them such as GBCs, but not so good for mechanisms that have variable loads such as vehicles. Overall, I'm pretty happy with it
I've only made fully detailed instructions for one of my models before (my Technic Water Strider), but I'm not very efficient at making them so they take me a long time to create.
I could create an MLCad file if someone else would be willing to turn that into instructions. Let me know if you want me to do this.

Hi Everyone.
I'd like to show you my GBC Module that I made called "To and Fro".
Definition:
to and fro /ˌto͞o ən ˈfrəo͝o/
adverb - in a constant movement backward and forward or from side to side.
verb - move constantly backward and forward.
noun - constant movement backward and forward.
I wanted to design a GBC module that I hadn't seen done before. The main feature of this design uses a string and pulley system, with different levels of mechanical advantage implemented to get the timing of the mechanisms just right.
This GBC module adheres to Type 1 of the GBC Standards, processing one ball per second on average (http://greatballcontraption.com/wiki/Standard).
The main focus of this module is the 'ladder' in the middle which raises and lowers using string and pulleys. You can see this in the video between 1:48 and 2:04, and I'll try to describe what is happening.
First of all, the end of the string is attached to the frame, and goes down to the cranks. The exact length of the string can be adjusted, similar to how guitar strings are tightened.
The cranks have pulleys on them, so the string actually moves twice as far as the diameter of the cranks as they rotate, but at the same time the force is halved.
Next, the string goes up to a pulley fixed on the frame, then down and around another pulley, and back up again. The bottom pulley is attached to the moving part of the 'ladder'. This halves the distance that the 'ladder' moves compared to the string, but also decreases the force required to do so.
The string goes over another static pulley at the top, and then back down to the outside edge of the moving part of the 'ladder'. To move the outside edge of the 'ladder' requires the full force of the string to move.
Due to the mechanical advantage of the different parts of the pulley system, the 'ladder' wants to move up first since this takes less force, but once it hits a stop at it's upper limit, the string then provides force to the outside edge of the 'ladder' which causes that last little 'kick', which lets the balls roll to the other side.
This module can also be broken down into four smaller sections for easier transportation:
The motor which is part of my Automatic Motor Shutoff and Alarm System,
The 'hopper' and 'ball diverter',
The 'ladder', and
The 'waterfall'.
There is only one M-motor powering this module and that helps ensure the timing of each section is in sync with the next.
The motor section is attached to the 'ladder' section with a universal joint, and the 'ladder' section is attached to the 'hopper' section with a CV joint.
The 'waterfall' section doesn't need any motor input, so it is attached to the 'ladder' section with a single axle that allows it to be detached easily.
Between the 'ladder' section and the 'hopper' section is differential (hidden away underneath), and I can manually adjust the rotation of this differential via a worm gear to get the timing between each section just right.
Apart from this one worm gear used to make timing adjustments, I haven't used any other worm gears as I have seen the damage they can do to GBC modules if something gets jammed (although, in theory, my Automatic Motor Shutoff and Alarm System should stop this from happening anyway).
There are quite a lot of gears within the drivetrain, but it runs quite smoothly. When I was creating it I thought the weight of the 'ladder' would cause a lot of strain on the motor, but when one side is going up gravity is making the other side go down which cancels out a lot of the strain.
Jams sometimes occur in the 'hopper' and 'ball diverter' sections, and are typically caused by too many balls in the hopper, or the timing of 'ball diverter' not being adjusted correctly.
I have had this running at a public expo that my LUG held, but I was too busy to baby-sit this module, so it was only running part of the time, but when it was running it ran without issue.
This is the first GBC module that I have made, so I spent a lot of time trying to get it working consistently. I hope you like it. Any constructive feedback/comments/questions are welcome.
UPDATE: I have created an LDraw/MLCad file of my GBC module. Read more here.
Music:

I used a total of 127 chain links. I would have tried to make this model bigger, but I was limited by the number of spare chain links that I had.
Instead of chain links, you could use string instead, and replace the gears with pulleys. As long as there is enough tension in the string (but not too much), string would probably end up being a bit smoother than chain links. I might try that out in the future sometime.

Hi Andy, thanks for your kind words.
I don't really have any other photos of this model at the moment, but the key parts are the six gears and the chain going around them with the sliding shuttle in the middle. Everything else is just me trying to build a working proof-of-concept by adding a frame, and cranks. Really, these can be added in any way that you like. The tires are just used to stabilize the model and provide grip so that it doesn't slide around the table. The size of my model was determined by the number of chain links that I had available. If you make it bigger, you may want to add something to put a little bit of tension on the chain. If you have any other questions, let me know and I'll provide more details where I can.

Hi everyone
It has been a little while since I have posted anything, but I wanted to share my latest model with you.
GoPro HERO Session Camera Dolly and Panning Rig
This model is a dual purpose dolly and panning rig for a GoPro HERO Session camera.
It uses a single chain to control both the linear movement of the camera (dolly) and/or the rotational movement of the camera (panning).
My YouTube video explains how this works in detail:
Please let me know what you think.
PS. For other models that I haven't posted on Eurobricks, please check out my YouTube channel (https://www.youtube.com/user/slfroden). Thanks